Investors are piling into US debt, signaling worry about economic growth and escalating trade tensions.

The yield on 10-year US Treasurys slid below 2% late Wednesday, falling to its lowest point since the November 2016 presidential election.

The downward slide came after the Fed held interest rates steady Wednesday and opened the door for rate cuts in the future, pending further escalation of the US-China trade war. The dovish policy is a swift reversal from the Fed's stance at the end of 2018, when it was on a rate-hiking path.

The decline comes for an unfortunate reason: investors are worried about economic growth. As those concerns rise, traders tend to flock to so-called haven assets such as the 10-year note.

In fact, the shift into these defensive bonds has reached the point where being long 10-year Treasurys was recently dubbed the "most crowded trade" in the June global fund manager survey conducted by Bank of America Merrill Lynch.

Escalating trade tension has also contributed to falling yields. The uncertainty around the US-China trade war is one of the biggest risks to global growth, so central banks are turning dovish to keep the expansion running. This has contributed to global yields falling, notably in the UK and Europe, which has also pushed the 10-year yield lower, said Ed Yardeni of Yardeni Research.

Abroad, Japan, Holland, Switzerland, and Denmark have already been in negative-interest-rate territory. Most recently, European Central Bank President Mario Draghi pledged on Tuesday to stimulate the eurozone if economic conditions don't improve.

That dovish stance sent the euro lower and earned the ire of President Trump, who accused Draghi of manipulating the Euro. In an environment where rates are falling, it can weaken the US dollar which can help other countries stabilize their own economies.